1. Field of the Invention
The present invention relates to a starter relay for use in a single-phase induction motor and so forth.
2. Description of the Related Art
A starter relay of this type may comprise a resistor 1 having a positive resistance temperature coefficient (PTC), which is pinched between a pair of contact springs 5, 6 in the form of separated V-shapes and housed in a container 2 of an electric insulator as shown in FIG. 4. This is well known as a starter relay 100X for a single-phase induction motor to drive a compressor incorporated in a household refrigerator (see Patent Document 1: JP-A 5-15178).
The resistor 1 may be made of barium titanate ceramics (Curie point: 130° C.), which has an electrical resistance that sharply increases when heated up to a certain temperature or higher.
The starter relay 100X is disposed as connected to an auxiliary winding of the single-phase induction motor. On starting of the single-phase induction motor, the temperature at the resistor 1 is low. Accordingly, the resistor 1 has a low electric resistance so that large starting current flows in the auxiliary winding to begin starting. The current flowing in the resistor 1 elevates the temperature by self-heating, which increases the electrical resistance, which lowers the current flowing in the auxiliary winding.
A starter relay 100Y having a structure shown in FIG. 5 is also well known (see Patent Document 2: JP-A 8-266076). In the starter relay 100X shown in FIG. 4, the resistor 1 is inserted between the contact springs 5, 6 while expanding the space between the contact springs 5, 6. In this case, the contact springs 5, 6 apply a pinching force against both sides of the resistor 1 from the time of insert. The force may damage the surface of the resistor 1 and cause a contact failure between the resistor 1 and the contact springs 5, 6 because of deflected opening of the contact springs 5, 6. In the starter relay 100Y, to the contrary, when a main container 2A and a lid container 2B are not integrated, a pair of contact springs 5, 6 has a small pinching force against the resistor 1. (Therefore, the resistor 1 can be installed between the contact springs 5, 6 with an easy work). On the other hand, when the main container 2A and the lid container 2B are integrated and protrusions 2C are fitted into required portions, the pair of contact springs 5, 6 applies a large pinching force for press-pinching the resistor 1. This starter relay 100Y is thus configured to solve the above problem associated with the starter relay 100X.
The starter relay 100X and the starter relay 100Y are structured such that the pair of contact springs 5, 6 pinching the resistor 1 from both sides can press and pinch surface-symmetrical sites of the resistor 1 from both sides. Accordingly, when the resistor 1 is broken, a broken fragment of the resistor is pinched between the pair of contact springs 5, 6. In this case, that portion radiates heat and elevates the temperature when power is supplied from terminals 7, 8, possibly resulting in production of smoke as a problem.